1. Field of the Invention
The present invention relates generally to apparatus and methods for cryosurgical therapy. In a particular embodiment, the invention provides a cryosurgical fluid delivery system which makes use of transients in the cooling cycle to moderate the cooling effects of a cryosurgical endovascular balloon catheter.
A number of percutaneous intravascular procedures have been developed for treating atherosclerotic disease in a patient""s vasculature. The most successful of these treatments is percutaneous transluminal angioplasty (PTA). PTA employs a catheter having an expansible distal end (usually in the form of an inflatable balloon) to dilate a stenotic region in the vasculature to restore adequate blood flow beyond the stenosis. Other procedures for opening stenotic regions include directional arthrectomy, rotational arthrectomy, laser angioplasty, stenting, and the like. While these procedures have gained wide acceptance (either alone or in combination, particularly PTA in combination with stenting), they continue to suffer from significant disadvantages. A particularly common disadvantage with PTA and other known procedures for opening stenotic regions is the subsequent occurrence of restenosis.
Restenosis refers to the re-narrowing of an artery following an initially successful angioplasty or other primary treatment. Restenosis typically occurs within weeks or months of the primary procedure, and may affect up to 50% of all angioplasty patients to some extent. Restenosis results at least in part from smooth muscle cell proliferation in response to the injury caused by the primary treatment. This cell proliferation is referred to as xe2x80x9chyperplasia.xe2x80x9d Blood vessels in which significant restenosis occurs will typically require further treatment.
A number of strategies have been proposed to treat hyperplasia and reduce restenosis. Previously proposed strategies include prolonged balloon inflation, treatment of the blood vessel with a heated balloon, treatment of the blood vessel with radiation, the administration of anti-thrombotic drugs following the primary treatment, stenting of the region following the primary treatment, and the like. While these proposals have enjoyed varying levels of success, no one of these procedures is proven to be entirely successful in avoiding all occurrences of restenosis and hyperplasia.
It has recently been proposed to prevent or slow reclosure of a lesion following angioplasty by remodeling the lesion using a combination of dilation and cryogenic cooling. Co-pending U.S. patent application Ser. No. 09/203,011, filed Dec. 1, 1998 the full disclosure of which is incorporated herein by reference, describes an exemplary structure and method for inhibiting restenosis using a cryogenically cooled balloon. While these proposals appear promising, the described structures and methods for carrying out endovascular cryogenic cooling would benefit from still further improvements. For example, the mechanical strength of the vasculature generally requires quite a high pressure to dilate the vessel during conventional angioplasty. Conventional angioplasty often involves the inflation of an angioplasty balloon with a pressure of roughly 10 bar. These relatively high pressures can be safely used within the body when balloons are inflated with a benign liquid such as contrast or saline. However, high pressures involve some risk of significant injury should the balloon fail to contain a cryogenic gas or liquid/gas combination at these high pressures. Additionally, work in connection with the present invention has shown that the antiproliferative efficacy of endoluminal cryogenic systems can be quite sensitive to the temperature to which the tissues are cooled: although commercially available, cryogenic cooling fluids show great promise for endovascular use, it can be challenging to reproducibly effect controlled cooling without having to resort to complex, high pressure, tight tolerance, and/or expensive cryogenic control components.
For these reasons, it would be desirable to provide improved devices, systems and methods for effecting cryosurgical and/or other low temperature therapies. It would further be desirable if these improved techniques were capable of delivering cryosurgical cooling fluids into the recently proposed endovascular cryosurgical balloon catheters, as well as other known cryosurgical probes. It would be particularly desirable if these improved techniques delivered the cryosurgical cooling fluid in a safe and controlled manner so as to avoid injury to adjacent tissues, ideally without requiring a complex control system and/or relying entirely on the operator""s skill to monitor and control these temperature-sensitive treatments.
2. Description of the Background Art
A cryoplasty device and method are described in WO 98/38934. Balloon catheters for intravascular cooling or heating of a patient are described in U.S. Pat. No. 5,486,208 and WO 91/05528. A cryosurgical probe with an inflatable bladder for performing intrauterine ablation is described in U.S. Pat. No. 5,501,681. Cryosurgical probes relying on Joule-Thomson cooling are described in U.S. Pat. Nos. 5,275,595; 5,190,539; 5,147,355; 5,078,713; and 3,901,241. Catheters with heated balloons for post-angioplasty and other treatments are described in U.S. Pat. Nos. 5,196,024; 5,191,883; 5,151,100; 5,106,360; 5,092,841; 5,041,089; 5,019,075; and 4,754,752. Cryogenic fluid sources are described in U.S. Pat. Nos. 5,644,502; 5,617,739; and 4,336,691. The following U.S. Pat. Nos. may also be relevant to the present invention: 5,458,612; 5,545,195; and 5,733,280.
The full disclosures of each of the above U.S. patents are incorporated by reference.
The present invention generally overcomes the advantages of the prior art by providing improved systems, devices, and methods for delivering cryogenic cooling fluid to cryosurgical probes, such as the new cryosurgical endovascular balloon catheters. The invention generally takes advantage of the transients during the initiation and termination of cryogenic fluid flow to moderate the treatment temperatures of tissues engaged by the probe. In some embodiments, a flow limiting element along a cryogenic fluid path intermittently interrupts the flow of cooling fluid, often cycling both the fluid flow and treatment temperature. This can help maintain the tissue treatment temperature within a predetermined range which is significantly above the treatment temperature which would be provided by a steady flow of cryogenic fluid. This intermittent flow may decrease sensitivity of the system to the particular configuration of the exhaust gas of flow path defined by a flexible catheter body disposed within the vascular system. Cooling of the vessel along the catheter body proximally of a balloon may also be decreased, thereby avoiding the embolization of frozen blood within the vasculature. In another aspect, the invention makes use of a single-use cooling fluid cartridges which may be transported safely at room temperature when filled with a sufficient quantity of cryosurgical fluid to effect a desired treatment, and which can be safely and cost-effectively disposed of after use.
In a first aspect, the invention provides a cryogenic fluid delivery system for use with a cryogenic probe having a cryogenic fluid input and a cooling surface for engaging a target tissue. The cryogenic delivery system comprises a cooling fluid container having a cryogenic fluid output. A cooling fluid path couples the fluid output of the container to the fluid input of the probe. A flow interrupter disposed along the cooling fluid path intermittently inhibits the flow of cryogenic cooling fluid from the container to the probe so as to limit cooling by the cooling surface.
A variety of flow interrupter structures may be used to moderate cooling of the target tissue. For example, the flow interrupter may comprise a solenoid valve, which will often be driven by a simple intermittent timing switch, a timing circuit, or the like. Alternatively, the flow interrupter may comprise a valve member rotatably engaging a valve body so as to provide fluid communication when the valve member is in a first rotational position and inhibit fluid communication when the valve is in a second rotational position. Such a rotatable valve assembly will often be driven by a motor, such as an electric motor, a pneumatic motor, or the like. Still further alternative fluid interrupters may comprise a deformable cryogenic conduit which can be occluded by actuation of a solenoid, pneumatic ram, or the like.
In another aspect, the invention provides a cryogenic fluid delivery system for use with a cryogenic probe. The probe has a cryogenic fluid input and a cooling surface, and the delivery system includes a cooling fluid container having a cryogenic fluid output. A cryogenic cooling fluid is disposed in the fluid container, and a cooling fluid path couples the fluid output of the container to the fluid input of the probe. Means are disposed along the cooling fluid path for limiting cooling of the cooled surface by intermittently inhibiting cooling fluid flow from the container to the probe.
In another aspect, the invention provides a single-use cryogenic fluid delivery system for use with a cryogenic endovascular catheter so as to inhibit hyperplasia of a diseased blood vessel region of a patient body. The cryogenic delivery system comprises a cooling fluid container and a connector for coupling to the catheter. A cooling fluid path provides fluid communication from the container to the connector. The path has a seal, and a cryogenic cooling fluid is disposed within the fluid container. The cooling fluid has a quantity and is at a pressure such that the catheter will cool the blood vessel to a temperature in a predetermined temperature range so as to inhibit hyperplasia when the connector is coupled to the catheter and the seal is opened.
Advantageously, the cryogenic fluid may be stored and transported at the desired pressure by the container when the container is at room temperature. The quantity of cryogenic fluid may be sufficient to maintain the blood vessel within the treatment temperature range for a time in predetermined treatment time range, thereby allowing the cooling system to be substantially self-controlling. Such a system is particularly useful for inhibiting hyperplasia or neoplasia, the quantity and pressure of the cryogenic fluid ideally being sufficient to cool a surface of the diseased blood vessel region to a temperature from about xe2x88x925xc2x0 C. to about xe2x88x9225xc2x0 C. for a time from about 10 to about 60 seconds, most often for a time between about 20 and 30 seconds.
The container will often comprise a disposable cartridge having a frangible seal. The seal may be breached by a fitting which threadably engages a casing in which the container is received. Such disposable cartridges can safely maintain cryosurgical cooling fluids such as N2O at high pressures and in sufficient quantities to effect a variety of desired treatments. For example, the cartridge may contain about 5 to 30 grams of cooling fluid, and may contain N2O or other cooling fluids at a pressure between about 400 and 1000 psi.
In a method aspect of the present invention, a tissue of a patient body can be treated using a cooling surface of a cryosurgical probe. Such a method may comprise coupling a cryogenic fluid canister to the probe, the canister containing a pressurized cryogenic cooling fluid. The cooling fluid flows from the canister toward the cooling surface of the probe. The flow is intermittently interrupted to limit cooling of the tissue by the probe.
The interruption periodically inhibits the flow of cooling fluid to avoid cooling of a tissue below a predetermined temperature range. This can repeatedly cycle a tissue temperature, ideally reaching a temperature within a range from about xe2x88x925xc2x0 C. to about xe2x88x9225xc2x0 C. for a time in a range from about 10 to about 60 seconds during the cycle, most often for a time between about 20 and 30 seconds. Typically, the cycling of the flow interruption and/or tissue temperature will have a period in a range from about 0.01 second to about 5 seconds, the frequency ideally being in a range from about 0.3 to about 3 hertz.
While this summary describes many of the optional, preferred features of the exemplary embodiments, it should be understood that the invention is not limited to these specific embodiments. A fuller understanding of the specific embodiments and their operation can be obtained with reference to the drawings and description which follow.